Physiological recording device

ABSTRACT

The present invention relates to a dry physiological recording electrode that can be used without skin preparation or the use of electrolytic gels. The dry physiological recording electrode comprising a substrate having an upper and a lower surface, and at least one penetrator(s) protruding from the upper surface of the substrate. The penetrator(s) is capable of piercing through the stratum corneum or outer layer of the skin, and transmitting an electric potential from the lower layers of the epidermis through the penetrator(s) which can be measured, or detecting agents from the lower layers of the epidmermis primarily the stratum germinativum layer. At least one epidermis stop may be provided resulting in the formation of detritus troughs interposed between adjacent penetrator(s) and epidermis stops. The present invention also includes a method of sensing biopotentials in the skin.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/906,234 filed on Oct. 1, 2007, which issued as U.S. Pat. No.7,489,959 on Feb. 10, 2009 and which was a continuation of U.S. patentapplication Ser. No. 11/401,559 filed on Apr. 11, 2006, which issued asU.S. Pat. No. 7,286,864 on Oct. 23, 2007 and which was a continuation ofU.S. patent application Ser. No. 10/874,075 filed on Jun. 22, 2004,which issued as U.S. Pat. No. 7,032,301 on Apr. 25, 2006 and which was acontinuation of U.S. patent application Ser. No. 09/949,044 filed onSep. 7, 2001, which issued as U.S. Pat. No. 6,785,569 on Aug. 31, 2004.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms provided for by the terms of grant number1R43 NS37631-01 awarded by the National Institute of NeurologicalDisorder and Stroke of the National Institute of Health and grant numberDMI-0109733 awarded by the National Science Foundation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a physiological recording electrodeand, more particularly, to a physiological recording electrode that canbe used without skin preparation or the use of electrolytic gels. Theinvention is further directed to penetrator with a size and shape whichthat will not bend or break, which limits the depth of application,and/or anchors the electrode or other device during normal application;and the use of stops which are integral with or separate from thepenetrator that adjust the depth of application of the penetrator,and/or allows for uniform application of the electrode or other deviceover unprepared skin.

2. Technical Background

Electrodes for measuring biopotential are used extensively in modernclinical and biomedical applications. These applications encompassnumerous physiological tests including electrocardiography (ECG),electroencephalography (EEG), electrical impedance tomography (EIT),electromyography (EMG) and electro-oculography (EOG). The electrodes forthese types of physiological tests function as a transducer bytransforming the electric potentials or biopotentials within the bodyinto an electric voltage that can be measured by conventionalmeasurement and recording devices.

In general, most commercial physiological electrodes for theseapplications today are placed on the surface of the skin. Because ofthis it is important to understand the anatomy of the skin to understandthe problems encountered with these electrodes. The skin is a layeredstructure, which consists of the epidermis and the dermis. The dermiscontains the vascular and nervous components. Further it is the part ofthe skin where pain has its origins. The epidermis is the most importantlayer in the electrode/skin interface. The epidermis consists of anumber of layers as shown schematically in FIG. 1. These layers consistof:

a) Stratum basale or stratum germinativum, which contains living basalcells, that grow and divide, eventually migrating into the other layersof the epidermis;

b) Stratum spinosum, which contains living cells that have migrated fromthe stratum basale. The early stages of desmosomes can be found in thislayer;

c) Stratum granulosum, which contains cells with many desmosomalconnections, forms a waterproof barrier that prevents fluid loss fromthe body;

d) Stratum lucidum, which is a transition layer between the stratumgranulosum and the stratum corneum. It is thickest in high frictionareas such as the palms and the soles of the feet; and

e) Stratum corneum, which is the outer layer, contains dry, dead cells,flattened to form a relatively continuous thin outer membrane ofrelatively continuous thin outer membrane of skin. The deeper cells ofthis layer still retain the desmosomal connections, but as they arepushed toward the surface by newly formed cells in the underlyinglayers, the junctions gradually break and the cells are lost.

The stratum corneum is the primary source of high electrical impedance.This is because dead tissue has different electrical characteristicsfrom live tissue, and has much higher electrical impedance. Thus, thislayer dramatically influences the biopotential measurements. The stratumcorneum is estimated to be approximately one tenth the thickness of theepidermis except for the palms of the hand and the foot where this layeris much thicker. The stratum corneum, further, is very thin and uniformin most regions of the body surface ranging from 13-15 μm with a maximumof about 20 μm. If the high impedance results from the stratum corneumcan be reduced, a more stable electrode will result. Therefore withexisting physiological electrodes the skin must be prepared prior toapplication when lower impedance is required.

The most common electrode preparation methods to avoid the highimpedance effects of the stratum corneum are: 1) shaving the hair fromthe skin; and either 2a) abrading the stratum corneum or 2b) using anelectrolytic gel. The use of an electrolytic gel or fluid is oftenreferred to as-“wet” electrodes. Hair is shaved from the skin to improvethe contact between the electrodes and the skin surface. The goal of theabrasion of the stratum corneum is to reduce the thickness of (orremove) the stratum corneum (and therefore its electrically insulatingcharacteristics). Drawbacks of abrading the skin are that the abradedarea regenerates dead cells fairly quickly (resulting in a limited timeperiod for using the electrode), and if the abrasion is too deep theperson can experience pain. Additionally, electrolytic gels or fluidsmay be applied to abraded surface to enhance the contact. Alternatively,electrolytic gels or fluids can be applied to the surface of the skindirectly. The electrolytic gel having a high concentration of conductiveions diffuses into the stratum corneum and improves its conductivity.Drawbacks observed with the use of electrolytic gels or fluids involvethe change of conductivity with time as the gels dry, discomfort (anitching sensation) at the patients skin as a result of the gels drying,and the possibility of a rash due to an allergic reaction to theelectrolytic gels.

Further drawbacks of “wet” electrodes include skin preparation andstabilization of the electrode with respect to the skin surface. This isbecause movement of the electrode on the surface of the skin causes thethickness of the electrolytic layer (formed by the electrolytic gels orfluids) to change resulting in false variation in the measuredbiopotential. Some electrode designs have an adhesive backing and/orgrated surfaces to reduce the movement of the electrode on the skinsurface, however, neither of these features eliminates completely themovement of the electrode with respect to the subject's skin. Anotherdrawback is the length of time required to prepare the skin and applythe electrolytic gels or fluids prior to measurement of thebiopotentials.

A less common type of physiological electrode is a non-polarizable “dry”electrode. These ceramic, high sodium ion conducting electrodes do notneed an electrolytic gel before their application. The principal of themeasurements from these physiological electrodes is based on a sodiumion exchange between the skin and the electrode. The skin-electrodeimpedance of these type of electrodes are found to decrease as afunction of application time. This is a result of perspiration beingproduced by the body under the electrode almost immediately afterapplication of the electrode on the skin. Drawbacks again, however,include many of those experienced with “wet” electrodes.

Another less common type of physiological electrode is an active “dry”electrode with an amplifier. Advances in solid-state electronictechnology have made it possible to record surface biopotentialsutilizing electrodes that can be applied directly to the skin withoutabrading the skin or using an electrolytic gel. These electrodes are notbased on an electrochemical electrode-electrolyte interface. Rather,these electrodes are active and contain a very high impedance-convertingamplifier. By incorporating the high impedance-converting amplifier intothe electrode, biopotentials can be detected with minimal or nodistortion. Although these electrodes offer the advantage of notrequiring some of the preparation needed with conventional electrodes,they have certain inherent disadvantages. These electrodes are bulky insize due to the additional electronics and power sources required andthey are typically more expensive to produce due to the electronicassembly required. Further, these electrodes also produce motionartifacts due to poor electrode-skin contact similar to electrodesrequiring electrolytic gels or fluids.

In view of the foregoing inherent disadvantages with presently availablewet and dry electrodes, it has become desirable to develop an electrodethat does not require skin preparation or the use of electrolytic gelsand overcomes the inherent disadvantages of presently available dryelectrodes.

SUMMARY OF THE INVENTION

The present invention is directed to a physiological recording electrodeand, more particularly, to a physiological recording electrode that canbe used without skin preparation or the use of electrolytic gels. Theinvention is further directed to penetrator with a size and shape whichthat will not bend or break, which limits the depth of application,and/or anchors the electrode or other device during normal application;and the use of stops which are integral with or separate from thepenetrator that adjust the depth of application of the penetrator,and/or allows for uniform application of the electrode or other deviceover unprepared skin.

In one embodiment, the present invention includes a dry physiologicalrecording electrode comprising a substrate, and at least penetrator(s)which is formed from a conductive coating and is protruding from thesubstrate wherein the penetrator(s) is capable of piercing the stratumcorneum or outer layer of the skin, and transmitting an electricpotential from the lower layers of epidermis through the penetratorwhich can be measured.

In another embodiment, the present invention includes a dryphysiological recording electrode comprising a thin metal sheet havingan upper and a lower surface, and at least one penetrator(s) protrudingfrom the upper surface of the thin metallic sheet wherein thepenetrator(s) from the thin metal sheet are capable of piercing throughthe stratum corneum layer or outer layer of the skin and transmitting anelectric potential from the lower layers of the epidermis through thepenetrator(s) which can be measured.

In another embodiment, the present invention includes a dryphysiological recording electrode comprising a silicon substrate havingan upper and a lower surface, and at least one penetrator(s) protrudingfrom the upper surface of the silicon substrate wherein thepenetrator(s) has a side(s) and a slope for the side(s) which issubstantially less than about 80 degrees along the side(s), and iscapable of piercing through the stratum corneum or outer layer of theskin and transmitting an electric potential from the lower layers of theepidermis through the penetrator(s) which can be measured.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate various embodimentsof the invention, and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Cross-sectional view of the epidermis layer of a person's skin.

FIG. 2. Cross-sectional view of the dry physiological recordingelectrode of the present invention.

FIG. 3. Cross-sectional view of the epidermis layer and an illustrationof the insertion of the penetrator(s) into the epidermis layer.

FIG. 4. Schematic of a process for micro-machining silicon electrodes.

FIG. 5. Sectioned side schematic view of dry penetrating recordingdevice.

FIG. 6 a. Illustration of dry penetrating recording device mounted tothe skin using an adhesive.

FIG. 6 b. Illustration of dry penetrating recording device mounted tothe skin using a harness.

FIG. 6 c. Illustration of dry penetrating recording device mounted tothe skin using a band.

FIG. 7. Flow chart illustrating methods of use of physiologicalrecording device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a dry penetrating recording device andpreferably a physiological recording electrode that does not require theuse of electrolytic gels or any type of skin preparation. Traditionally,the monitoring of animal and in particular human physiological data hasrequired that electrodes be attached to the skin with adhesive collars,tape or collodion after the skin has been vigorously cleaned to reducethe contact impedance. This approach is both time consuming andtroublesome. With the advent of small portable physiologic recordingdevices, it has become possible to record data from individuals in-situ.It has also become feasible to conduct routine real-time monitoring oftest subjects in a variety of environments. To fully exploit thecapability of these portable physiological recording devices, an easy touse dry recording electrode similar to the present invention isrequired.

One embodiment of the present invention is shown in FIG. 2. Thisembodiment is a cross-sectional view of a portion of the dryphysiological recording electrode 10. The dry physiological recordingelectrode 10 is comprised of a substrate 12 having an upper surface 14and a lower surface 13. The upper surface 14 of the substrate 12comprising at least one penetrator(s) 16 sized and shaped for piercingthe stratum corneum or outer layer of the epidermis, and accessing thelower layers of the epidermis. The penetrator 16 can take many shapesincluding but not limited to pyramidal, needle-like, triangular, or anyother shape that can be tapered to a point or tip.

Preferably, the size and shape of the penetrator 16 is such that thepenetrator(s)16 will not break or bend during normal use, will limit thedepth the penetrator enters the skin under typical applicationconditions, and/or will anchor the electrode 10 to prevent motionartifacts or any substantial movement. Therefore, preferably, theappropriate aspect ratio of the height to the average width of thepenetrator 16, slope of the edge(s) or side(s) of the penetrator 16,and/or height of the penetrator 16 are selected to make an electrode 10wherein the penetrator(s) 16 will not break or bend, and will betteranchor the electrode 10 during application. The height of thepenetrator(s) is measured from the tip of the penetrator 16perpendicular to the substrate 12. The penetrator(s) 16, preferably, hasa height from about 20 to about 150 μm, and more preferably from about40 to about 100 μm. The aspect ratio of the penetrator is ratio of theheight divided by the average width of the penetrator. The average widthof the penetrator 16 is measured by taking the widest averagecross-section dimension of the cross-sections of the penetrator 16perpendicular to the height. The penetrator(s) 16, preferably, has anaspect ratio of less than about 5, more preferably of less than about 2,even more preferably of less than about 1.5 and most preferably of lessthan about 0.75. The slope of the edge(s) or side(s) of the penetrator16 is measured by drawing a line tangent to the edge or the side of thepenetrator(s) at any given point to the substrate 12 and measuring theangle between the line and where it intersects the upper surface 14 ofthe substrate. While it is understood that the slope may or may not varysubstantially along the edge or side of the penetrator(s), preferablythe slope is less than about 80 degrees over substantially all of theedge or side of the penetrator 16, more preferably is less than about 70degrees, and most preferably is less than about 60 degrees. Bysubstantially all of the edge or side of the penetrator, it is meantthat 60% of the length of the edge or side has a slope less than thatset forth above. However, preferably, 75% of the length of the edge orside has a slope of less than that set forth and more preferably 90% ofthe length of the edge or side has a slope of less than that set forth.For this application, in the case of penetrator(s) 16 etched from thinsheets of material preferably a metal having a thickness of less thanabout 2 mm, the slope of the edge or side is always measuredperpendicular to the thickness of the sheet metal.

FIG. 3 is a schematic illustrating the insertion of the penetrator(s)into the epidermis. The penetrator(s) 16 are used to push through thehigh impedance upper layer or stratum corneum of the epidermis to reducethe contact impedance of the electrode. Preferably, the penetrator(s) 16also “lock” the electrode into the chosen skin region and thus reducemotion artifacts. The penetrator(s) 16 are further used forphysiological sensing in the lower layers of the epidermis. The lowerlayers of the epidermis include the other layers below the stratumcorneum of the epidermis. Physiological sensing generally is the sensingof electric potentials. The penetrator(s) 16 are used transmit theelectric potential from the lower layers of the skin, particularly theepidermis and more particularly the stratum germinativum layer of theepidermis. The electric potential then can be measured by conventionalmeasuring devices.

Preferably, the surface of the penetrators 16 in contact with the skinfor the dry physiological electrode 10 of the present invention aresubstantially non-chemically reactive with the chemicals in the skin andin particular the epidermis of the skin including NaCl, other chemicalsand biological agents. By substantially non-chemically reactive it ismeant that the majority of electric voltage (or potential) from theelectrode isn't generated by the corrosion or through the deposition ofmaterials on the surface of the penetrators 16 (similar to a chemicalcell or battery). More preferably, less than about 30% of the electricvoltage generated and transformed by the electrode is created bycorrosion of the penetrators 16, even more preferably less than about10%, and most preferably less than about 2%.

Epidermis stops 18 and detritus troughs 20 may also be provided on theupper surface 14 of the substrate 12. The detritus troughs 20 are theareas interposed between adjacent epidermis stops 18, adjacentpenetrators 16 or adjacent epidermis stops 18 and penetrators 16. Thesetroughs 20 when provided allow for a more accurate placement of thepenetrator(s) 16 by allowing for displacement of the hair and otherdetritus on the skin in these troughs 20. Preferably, the detritustroughs 20 are sufficient in number and size to allow for placement ofthe electrode 10 on skin with a significant amount of hair such as forexample the scalp or the chest of a male subject. Further preferably,the distance between the adjacent epidermis stops 18 and penetrator(s)16 or adjacent penetrators 16 is at least 80 μm at their nearest points,more preferably at least 160 μm and most preferably at least 250 μm.Preferably, the shape of the penetrators 16 are such that they functionas an epidermal stop by effectively limiting the depth of penetration ofthe penetrator 16 into the skin due to their shape and typical pressuresand/or application techniques used when applying the packaged electrode10 to the skin.

If provided, the epidermis stops 18 are of a particular height withrespect to the height of the penetrator(s) 16 so as to prevent thepenetrator(s) 16 from penetrating into the dermis of the skin where theymight cause discomfort to the subject. In maximizing the area of thedetritus troughs 20 that is available for optimal electrode to skincontact, while improving the probability that hair and other detrituswill enter the troughs 20, the epidermis stops 18 preferably have asemi-circular shape in cross-section (not shown). The epidermis stops 18may, however, have any shape know to those skilled in the art that wouldeffectively prevent the penetrator(s) 16 from entering the dermis of theskin. Furthermore, the epidermis stops 18 are preferably applied in anarray between each of the penetrator(s) 16, therefore further minimizinginadvertent deep penetration or over penetration by the penetrator(s).

Another embodiment of the present invention includes a dry penetratingrecording device for measuring biological characteristics orbiopotential (electric potential) from the lower layers of theepidermis. Shown in FIG. 5, this device comprises a substrate having anupper and a lower surface, at least one penetrator(s) 16 protruding fromthe upper surface of the substrate. Optionally, the device can furthercomprise at least one epidermal stop(s). The penetrator(s) and epidermalstop(s) for the device have similar characteristics such as size andshape to those described above for use with dry physiologicalelectrodes.

The dry penetrating recording device 30 and the dry physiologicalelectrode 10 of the present invention can be formed from a variety ofprocesses and materials known to those skilled in the art. The substrate12 from which the penetrators 16 are formed or to which they are addedcan by way of example but not limitation be made from the following:conductive metal sheet and conductive metals including for examplestainless steel, nickel and copper; semi-conductive metal including forexample silicon and doped silicon wafers; ceramics including for exampleoxides; and polymers including for example electrically insulatingpolymers such as polyimides. Preferably, all non-conductive substratesare coated or doped to make the substrate semi-conductive or conductive.There are however in general four processes by which embodiments of thepresent invention are preferably manufactured.

The first process is where the electrode 10 can be formed from metalsheet through photo micro-machining techniques. These techniques can beused to form the penetrator(s) 16 (and epidermis stops 18 and springs,if desired). With this process one edge of a thin gauge stock of metal,preferably stainless steel, is photo defined and chemically etched,effectively forming a thin cross section of a desired two dimensionalsurface containing at least one penetrator(s) 16 and, if desired,epidermis stops 18 and springs (not shown) on the lower surface. At thispoint various film layers, specific coatings and leads can be coated ordeposited onto the electrode to make it individually addressable or tofunction as desired in an array. This forms an electrode 10 with a crosssection with approximately the thickness of the thin gauge metal stock.Stainless steel is preferred because of its good biocompatibility,excellent corrosion resistance, and because of its ability to be cleanedand reused, however, a variety of other materials know in the art canalso be used. An electrode array can be formed by stacking or laminatingmany of these thin strip electrodes 10 together. Additionally, lasermachining, abrasion and other metal working techniques may be used toproduce the electrode 10.

For the second process the electrode 10 can be formed from siliconwafers, preferably (100) silicon wafers are used. FIG. 4 is a schematicshowing the major process steps for silicon based micro machined dryelectrode fabrication. In the first step of this process, an oxide layer22 is formed on the silicon wafer 21. Following growth of the oxidelayer 22, a photo resist (not shown) is applied and the pattern 23 forthe major electrode peaks is transferred using a conventional photoresist process. Following application of the photo resist, the wafers 21etched to form mesas 24 at what will ultimately become pyramidalelectrode peaks. If epidermis stops 18 are not desired then furtheretching of the wafer 21 takes place to form the pyramidal electrodepeaks. If, however, epidermis stops 18 are desired, following theanisotropic etch, the surface of the silicon wafer 21 is stripped of alloxides and masking material. Again, another oxide layer 25 is formed onthe silicon wafer 21. Following the growth of the oxide layer 25, afairly thick photo resist 26 is applied to the upper surface of thesilicon wafer 21. Again, the photo resist is masked with a pattern 27but this time for the epidermis stops. Then a second bulk anisotropicetch is used to form the epidermis stops and to finish thepenetrator(s). After etching is completed, the remaining oxide isremoved. At this point, the silicon optionally can be doped to increasethe conductivity of the electrode, and also various film layers andleads can be coated onto the electrode to make it individuallyaddressable or to function as desired in an array of electrodes 10.

With the third process the electrode 10 can be formed by an additivedeposition process. Preferably, an electroplating process is used.Preferably, the substrate for this process is a flexible polymer, andmore preferably an insulating polymer such as a polyimide. With thisprocess a thin layer of metal is applied to the substrate. Then a thicklayer of photo resist is applied to the thin layer of metal on thesubstrate and patterned by photolithography to create the desiredfeatures, i.e., arrays of squares, circles, etc. These patterns form thebase of the electrodes and the other features of the electrode array.The photo resist is stripped from the substrate. Another layer ofphotoresist is applied. These patterns further define the penetratorstructure which is built up to the desired height and shape byelectroplating. Optionally, at this point various film layers and leadscan be coated onto the electrode to make it individually addressable orto function to improve the conductivity as desired in an array ofelectrodes 10.

With the fourth process the electrode 10 may be formed by injectionmolding, casting or depositing a material into a mold. A mold with theimprint or negative image of the desired surface features which mayinclude the penetrators, detritus troughs and epidermis stops is formed.This mold may be filled via injection molding, casting, deposition orother material forming technique to produce the desired electrode 10.Optionally and as a function of the conductivity of the materialutilized, the surface may be doped to increase the conductivity of theelectrode, and also various film layers and leads can be coated onto theelectrode to make it individually addressable or to function as desiredin an array of electrodes 10.

The electrodes of the present invention can be used in a variety ofapplications including but not limited to ECG, EEG, EIT, EMG, and EOG.The electrodes can be packaged by conventional packaging techniques,however, preferably the package 31 provides 1) adequate structuralsupport for the electrode so it can be handled roughly (i.e., dropped,crushed, etc,) without damage; 2) a means (i.e., a spring 32, etc,) toforce the electrode against the subject's skin with a consistentpressure; 3) a low impedance path 33 from the electrode's surface to thepackage's output connector 34; and 4) a design which allows for easycleaning and sterilization for applications requiring reuse. Theseelectrode packages also can be mounted to the skin using conventionaltechniques such as adhesives 35, harnesses 40 or bands 45, as shown inFIG. 6.

The dry physiological recording electrodes 10 are applied to an animalor human body having skin comprising an epidermis comprising a stratumcorneum layer and lower layers of the epidermis, and a dermis. Thepenetrator(s) 16 of the electrode 10 pierce through the stratum corneumlayer of the skin with the penetrator(s) such that the penetrator(s)does not enter the dermis of the skin. The penetrator(s) 16 senses theionic current in the lower layers of the epidermis, and transforms aportion of the ionic current of the lower layers of the epidermis of theskin into an electric voltage through the penetrator(s) 16. The electricvoltage from the penetrator(s) 16 is measured using conventionalmeasuring devices.

FIG. 7 illustrates methods of acquiring physiological signals from asubject according to the present invention. In one embodiment, at leastone dry electrode is formed 50 from a negative image having desiredsurface, where said surface features include at least one penetratorsized and shaped for piercing the stratum corneum or outer layer of theepidermis and accessing the lower layers of the epidermis. In anotherembodiment, a physiological electrode with at least one surface featureis formed 51 from an image having desired surface features, where the atleast one surface feature is sized and shaped for accessing the lowerlayers of the epidermis. In yet another embodiment, at least onephysiological electrode with at least one surface feature is formed 52from an image having desired surface features, where the at least onesurface feature is sized and shaped for accessing the lower layers ofthe epidermis. Preferably, the penetrator or surface feature has anaspect ratio of less than about 1.5. Further preferably, at least twopenetrators or surface features are formed on the surface of the dryelectrode, and they are individually addressable. Optionally, a film orcoating may be applied 53 to the surface of the electrode before theelectrode is packaged 54 with a portable physiological recording deviceor packaged 55 with an output connector. The packaged electrode is thenplaced 56 in contact with the skin of the subject, where it may bemounted with adhesives, harnesses, bands, or any other conventionaltechniques, and a physiological signal is thereby acquired from thesubject 57. The physiological signal acquired may be, for example, ECG,EEG, EIT, EMG, or EOG.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of acquiring physiological signals from a subject havingskin comprising forming at least one dry electrode from a negative imagehaving desired surface features, where said surface features include atleast one penetrator sized and shaped for piercing the stratum corneumor outer layer of the epidermis and accessing the lower layers of theepidermis, packaging the at least one dry electrode with a portablephysiological recording device wherein the at least one dry electrode iscapable of transmitting a signal to the recording device, placing the atleast one dry electrode in contact with the skin of the subject, andacquiring a physiological signal from the subject.
 2. The method ofclaim 1, wherein the at least one penetrator has an aspect ratio of lessthan about 1.5.
 3. The method of claim 1, wherein the physiologicalsignal acquired is ECG.
 4. The method of claim 1, wherein at least twopenetrators are formed on the surface of the dry electrode, and the atleast two penetrators are individually addressable.
 5. The method ofclaim 1, further including the step of applying a film or coating to thesurface of the dry electrode.
 6. A method of acquiring physiologicalsignals from a subject having skin comprising forming a physiologicalelectrode with at least one surface feature from an image having desiredsurface features, where the at least one surface feature is sized andshaped for accessing the lower layers of the epidermis, packaging thephysiological electrode with a portable physiological recording devicewherein the physiological electrode is capable of transmitting a signalto the portable physiological recording device, placing thephysiological electrode in contact with the skin of the subject, andacquiring a physiological signal from the subject.
 7. The method ofclaim 6, wherein the at least one surface feature has an aspect ratio ofless than about 1.5.
 8. The method of claim 6, wherein the physiologicalsignal acquired is an ECG signal.
 9. The method of claim 6, wherein atleast two surface features are formed on the surface of thephysiological electrode, and the at least two surface features areindividually addressable.
 10. The method of claim 6, further includingthe step of applying a film or coating to the surface of the dryelectrode.
 11. A method of acquiring physiological signals from asubject having skin comprising forming at least one physiologicalelectrode with at least one surface feature from an image having desiredsurface features, where the at least one surface feature is sized andshaped for accessing the lower layers of the epidermis, packaging the atleast one physiological electrode to provide a low impedance path fromthe electrode's surface to the package's output connector, placing theat least one physiological electrode in contact with the skin of thesubject, and acquiring a physiological signal from the subject.
 12. Themethod of claim 11, wherein the physiological signal acquired is an ECGsignal.
 13. The method of claim 11, wherein the package is mounted tothe subject's skin with adhesives.
 14. The method of claim 11, whereinat least two surface features are formed on the surface of thephysiological electrode, and the at least two surface features areindividually addressable.